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// Copyright 2017, 2018 Parity Technologies
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::{Error, Decode};

/// The error message returned when `decode_all` fails.
pub(crate) const DECODE_ALL_ERR_MSG: &str = "Input buffer has still data left after decoding!";

/// Extension trait to [`Decode`] that ensures that the given input data is consumed completly while
/// decoding.
pub trait DecodeAll: Sized {
	/// Decode `Self` and consume all of the given input data.
	///
	/// If not all data is consumed, an error is returned.
	fn decode_all(input: &[u8]) -> Result<Self, Error>;
}

impl<T: Decode> DecodeAll for T {
	fn decode_all(input: &[u8]) -> Result<Self, Error> {
		let input = &mut &input[..];
		let res = T::decode(input)?;

		if input.is_empty() {
			Ok(res)
		} else {
			Err(DECODE_ALL_ERR_MSG.into())
		}
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use crate::{Encode, Input, Compact, EncodeLike};

	macro_rules! test_decode_all {
		(
			$( $type:ty => $value:expr; )*
		) => {
			$(
				{
					let mut encoded = <$type as Encode>::encode(&$value);
					<$type>::decode_all(&encoded).expect(
						&format!("`{} => {}` decodes all!", stringify!($type), stringify!($value)),
					);

					encoded.extend(&[1, 2, 3, 4, 5, 6]);
					assert_eq!(
						<$type>::decode_all(&encoded).unwrap_err().to_string(),
						"Input buffer has still data left after decoding!",
					);
				}
			)*
		};
	}

	#[derive(Debug)]
	struct TestStruct {
		data: Vec<u32>,
		other: u8,
		compact: Compact<u128>,
	}

	impl EncodeLike for TestStruct {}

	impl Encode for TestStruct {
		fn encode(&self) -> Vec<u8> {
			let mut res = Vec::new();
			self.data.encode_to(&mut res);
			self.other.encode_to(&mut res);
			self.compact.encode_to(&mut res);
			res
		}
	}

	impl Decode for TestStruct {
		fn decode<I: Input>(input: &mut I) -> Result<Self, Error> {
			Ok(
				Self {
					data: Vec::<u32>::decode(input)?,
					other: u8::decode(input)?,
					compact: Compact::<u128>::decode(input)?,
				}
			)
		}
	}

	#[test]
	fn decode_all_works() {
		test_decode_all! {
			u8 => 120;
			u16 => 30;
			u32 => 1;
			u64 => 2343545;
			u128 => 34358394245459854;
			Vec<u8> => vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
			Vec<u32> => vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
			Compact<u32> => Compact(32445);
			Compact<u128> => Compact(34353454453545);
			TestStruct => TestStruct { data: vec![1, 2, 4, 5, 6], other: 45, compact: Compact(123234545) };
		}
	}
}